Septic tanks, whether made of synthetic materials obtained by moulding or via brickwork, are used to recover degradable materials but are also often used to collect domestic sewerage originating from runoffs, from washbasins, sinks, machines, etc., as it clearly being much simpler to avoid providing a runoff collector by the side of a house. Up until now, a degradable substances intake pipe usually has been provided at one extremity of the tank and an outlet to the irrigation zone at the opposite extremity so that decantation, fermentation of the organic degradable substances and the flotation of sludge is effected correctly inside the tank. When the tank is required to also recover sewerage water, it is more suitable to direct these towards the degradable substances intake pipe or directly towards the tank from a waste water collector situated further away, this system thus involving the need for additional work to be carried out.
The inventor has found that it would be much easier to incorporate inside a prefabricated septic tank a sole collector for collecting the the degradable substances and also waste water which can be inspected by means of a single chamber and which accordingly overcomes those drawbacks relating to known solutions. This integration proves to be advantageous in that it concerns the adjacent incorporation of an interchangeable cartridge anticlogging prefilter system, such as the one described in FR-A 2 610 653. Thus, a single-block tank is provided which is able to directly receive all intake pipes for intaking fluid originating from all directions.